Projector and image correction method

ABSTRACT

A projector displays an image on a projection surface. The projector has a zoom adjusting module and a keystone correcting module. The zoom adjusting module adjusts zoom level of a zoom lens for enlarged projection of image light. The keystone correcting module corrects trapezoidal distortion of the image displayed on the projection surface by means of forming the effective panel image in a revised image formation area, the revised image formation area being part of the image formation area of the panel surface.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the priority based on Japanese PatentApplication No. 2004-178112 filed on Jun. 16, 2004, the disclosure ofwhich is hereby incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projector for projecting light onto ascreen or other projection surface to display an image, and inparticular relates to a technique for executing zoom adjustment andkeystone correction.

2. Description of the Related Art

When an image is displayed on a projection surface such a screen using aprojector, trapezoidal distortion sometime occurs in the image displayedon the projection surface (hereinafter termed “display image”) due tothe relative positions of the projector and the projection surface. Insuch instances, keystone correction is used to correct trapezoidaldistortion of the display image.

Keystone correction is carried out by reducing the image to trapezoidalshape and forming the image on the liquid crystal panel of theprojector, and thus when there is appreciable trapezoidal distortion ofthe display image, the image formed on the liquid crystal panel becomessmall, resulting in some instances in a drop in image resolution.

In the meanwhile, projectors are equipped with a zoom lens for adjustingthe size of the display image on the projection surface. By adjustingthe zoom lens (hereinafter referred to as “zoom adjustment”), zoom levelcan be adjusted between the telephoto end (smaller display image end)and the wide angle end (larger display image end). When a display imageis displayed on the projection surface using the projector, it ispreferred that a display image is displayed as large as possible on theprojection surface.

Various techniques have been disclosed for performing zoom adjustmentand keystone correction automatically, while avoiding a drop inresolution. For example, there has been disclosed a technique inJP2000-241874A whereby a test pattern is displayed on the projectionsurface and captured with a monitor camera, the image so captured beingused to carry out zoom adjustment such that the largest possible displayimage is displayed automatically on the projection surface; and keystonecorrection is then performed. There has also been disclosed a techniquein JP8-292496A whereby a test pattern is displayed on the projectionsurface, and zoom adjustment is then carried out while determiningwhether the pattern has reached maximum size within the projectionsurface.

However, with the prior art mentioned above, since keystone correctionis performed after zoom adjustment to display the display image atmaximum size on the projection surface, the display image on theprojection surface is reduced due to keystone correction, becomingsmaller in size. This causes necessity of repeating zoom adjustment.

An additional problem is that conventional zoom adjustment such as thatdescribed above is executed repeatedly through process of projecting atest pattern, capturing it with a monitor camera, making adetermination, and performing zoom adjustment, until the intended zoomlevel is determined, making the process very time consuming.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a technique wherebywhen projecting an image onto a projection surface with a projector, itis possible to carry out zoom adjustment and keystone correction rapidlyand automatically, while avoiding drop in resolution.

In one aspect of the present invention, there is provided a projectorwhich displays an image on a projection surface. The projector comprisesa light source, an image formation panel, a zoom adjusting module, and akeystone correcting module. The light source emits light. The imageformation panel forms in an image formation area of a panel surface aneffective panel image for modulating light emitted by the light sourceinto effective image light representing an image. The zoom adjustingmodule adjusts zoom level of a zoom lens for enlarged projection ofimage light. The keystone correcting module corrects trapezoidaldistortion of the image displayed on the projection surface by means offorming the effective panel image in a revised image formation area, therevised image formation area being part of the image formation area ofthe panel surface. The zoom adjusting module adjusts the zoom level to atarget zoom level in which a total projection area encompasses theprojection surface and in which a perimeter of the total projection areacontacts the perimeter of the projection surface at one or more contactpoints, the total projection area being an area onto which is projectedimage light corresponding to all areas of the image formation area ofthe panel surface. The keystone correcting module performs correctionsuch that the perimeter of the revised image formation area contacts theperimeter of the image formation area of the panel surface at a point onthe perimeter of the image formation area of the panel surfacecorresponding to the contact point of the perimeter of the totalprojection area with the perimeter of the projection surface.

With this projector, since keystone correction is carried out in such away that the perimeter of the revised image formation area contacts theperimeter of the image formation area of the panel surface, a revisedimage formation area of large size can be set, and drop in resolution ofthe effective panel image can be avoided. Additionally, since zoomadjustment is carried out in such a way that the total projection areaincludes the projection surface, a larger display image can be displayedon the projection surface, and keystone correction to correcttrapezoidal distortion can be carried out.

The present invention can be realized in a various aspects. For example,the present invention can be realized in aspects such as a projector, animage projection method and device, an image correction method anddevice, a zoom adjustment method and device, a keystone correctionmethod and device, a computer program for effecting the functions ofsuch methods or devices, a recording medium for recording such acomputer program, and data signals in which such a computer program iscarried on the carrier wave.

These and other objects, features, aspects, and advantages of thepresent invention will become more apparent from the following detaileddescription of the preferred embodiments with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the structure of a projector asembodiment 1 of the present invention.

FIGS. 2( a) and 2(b) are diagrams showing the relationship of the liquidcrystal panel 130 and the image formation area IF.

FIG. 3 is a flowchart showing the flow of the zoom adjustment/keystonecorrection process.

FIGS. 4( a) to 4(c) are diagrams showing an example of projectionconditions during projection of a total projection area detectionpattern.

FIGS. 5( a) and 5(b) are diagrams showing conception of projectivetransformation of the total projection area frame PFi and the screenframe 202 i.

FIGS. 6( a) to 6(c) are diagrams showing an example of projectionconditions after the zoom adjustment/keystone correction process.

FIGS. 7( a) to 7(e) are diagrams showing conception of calculation ofbest zoom level.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Next, aspects of the present invention will be described in thefollowing order on the basis of embodiments:

A. Embodiment 1

A-1. Structure of Projector

A-2. Zoom Adjustment/Keystone Correction Process

B. Variations

A. Embodiment 1

A-1. Structure of Projector

FIG. 1 is a block diagram showing the structure of a projector asembodiment 1 of the present invention. This projector 100 projects imagelight representing an image onto a screen 200 or other projectionsurface to display an image (display image). The projector 100 comprisesan A/D converter 110, internal memory 120, a liquid crystal panel 130, aliquid crystal panel driver 132, an illumination optical system 140, aprojection optical system 150 that includes a zoom lens 152, a zoom lensdriver 154, a zoom level detector 156, a CPU 160, a remote control unitcontroller 170, a remote control unit 172, a capture module 180, and acaptured image memory 182.

The internal memory 120, liquid crystal panel driver 132, zoom lensdriver 154, zoom level detector 156, CPU 160, remote control unitcontroller 170, and captured image memory 182 are interconnected througha bus 102.

The A/D converter 110 performs A/D conversion of an input image signalinput from a DVD player or PC (not shown) via a cable 300, to convert itto a digital image signal.

In the internal memory 120 is stored a computer program that functionsas an image processor 122. The image processor 122 performs adjustmentof image display parameters (e.g. luminance, contrast, sync, tracking,color density, tint etc.) on the digital image signal output by the A/Dconverter 110, and outputs the resultant signal to the liquid crystalpanel driver 132.

The image processor 122 also includes the functions of an image regiondetector 123, a best zoom level calculator 124, a zoom adjustment module125, a keystone correction module 126, and a standard transformationmodule 127; the zoom adjustment/keystone correction process describedlater is carried out by means of these functions.

The liquid crystal panel driver 132 drives the liquid crystal panel 130based on the digital image signal input from the image processor 122. Onan image formation area IF of the surface (panel surface) of the liquidcrystal panel 130, the liquid crystal panel 130 forms a panel image forthe purpose of modulating illumination emitted by illumination opticalsystem 140 into image light representing an image. FIGS. 2( a) and 2(b)are diagrams showing the relationship of the liquid crystal panel 130and the image formation area IF. The image formation area IF refers tothe area on the panel surface of the liquid crystal panel 130 where thedigital image signal input to the liquid crystal panel driver 132 can bedisplayed. As shown in FIG. 2( a), the image formation area IF of thisembodiment is established in an area smaller by about 2 dots on all foursides than the total panel surface of the liquid crystal panel 130. Thesize of the image formation area IF with respect to the total panelsurface of the liquid crystal panel 130 may be established arbitrarily.During keystone correction described in detail later, the image to beprojected may be formed in an area which is part of the image formationarea IF of the liquid crystal panel 130, with a wholly black imageformed in other areas. The area of this portion of the image formationarea IF is termed the “revised image formation area RIF.” The image fordisplay formed in the revised image formation area RIF is termed the“effective panel image.”

In the event that, for example, the resolution of the input digitalimage signal is lower than the resolution of the liquid crystal panel130, with the input digital image being displayed as is withoutenlargement, the image formation area IF will be established in an areasmaller than the total surface of the liquid crystal panel 130, inassociation with the ratio of the two resolutions, as shown in FIG. 2(b).

The projection optical system 150 (FIG. 1) is mounted on the front ofthe projector 100 housing, and functions to enlarge and project lightthat has been modulated into image light by the liquid crystal panel130. The zoom lens driver 154 drives the zoom lens 152 provided in theprojection optical system 150, to change the zoom level. Here, zoomlevel refers to the extent (magnification) of enlargement in theprojection optical system 150 when projecting light that has passedthrough the liquid crystal panel 130. That is, the zoom lens driver 154varies the size of the display image displayed on the screen 200.

The zoom level detector 156 detects the zoom level of the zoom lens 152.Specifically, the zoom level detector 156 includes a variable resistancewhose resistance value varies in association with adjustment of the zoomlens 152 and an A/D converter that converts resistance values of thevariable resistance to digital values. The zoom level detector 156detects zoom level based on resistance values in digital value form(hereinafter termed “zoom encoder values”). In this embodiment, zoomlevel is represented by a zoom level value. Zoom level value isestablished assigning a baseline value of 1 to the value of the zoomlevel at which the display image is at its smallest size (hereinaftertermed “baseline zoom level”). Zoom level value of any zoom level isrepresented as the ratio of magnification of the display image in thezoom level to that in the baseline zoom level. The relationship betweenzoom encoder value and zoom level value is measured in advance andstored in a predetermined area of the internal memory 120.

The remote control unit controller 170 receives commands from a user viathe remote control unit 172 and relays the commands to the CPU 160 viathe bus 102. In this embodiment, the projector 100 is designed toreceive user commands through the remote control unit 172 and remotecontrol unit controller 170, but it would be possible instead to haveanother arrangement for receiving user commands, such as a control panelfor example.

The CPU 160, by reading the computer program that functions as the imageprocessor 122 from the internal memory 120 and executing the program,projects an image onto the screen 200 and performs image processing suchas the zoom adjustment/keystone correction process described later. TheCPU 160 also controls operation of the various parts of the projector100.

A-2. Zoom Adjustment/Keystone Correction Process

The projector 100 performs a zoom adjustment/keystone correction processto carry out zoom adjustment and keystone correction automatically. Zoomadjustment is a process for carrying out adjustment of zoom level sothat the projected image is displayed as large as possible withoutrunning off the edges of the screen 200. Keystone correction is aprocess for correcting trapezoidal distortion of the display image onthe screen 200. The zoom adjustment/keystone correction process beginsto execute when user command is made through the remote control unit172. The zoom adjustment/keystone correction process may begin toexecute automatically, for example, when the power is turned on, or whenan image signal is input.

FIG. 3 is a flowchart showing the flow of the zoom adjustment/keystonecorrection process. In Step S402, the image processor 122 (FIG. 1)projects a total projection area detection pattern. Total projectionarea refers to an area on the screen 200 or on the wall behind thescreen 200 onto which is projected image light corresponding to allareas in the image formation area IF (FIG. 2( a)) of the liquid crystalpanel 130. Image light corresponding to all areas in the image formationarea IF of the liquid crystal panel 130 refers to the image lightprojected when the effective panel image is formed in all areas of theimage formation area IF of the liquid crystal panel 130.

FIGS. 4( a) to 4(c) are diagrams showing an example of projectionconditions during projection of a total projection area detectionpattern. The condition of the liquid crystal panel 130 is shown in FIG.4( a). In this embodiment, an entirely white pattern is used as thetotal projection area detection pattern. Consequently, a panel image(effective panel image) of the white pattern is formed over all areas ofthe image formation area IF of the liquid crystal panel 130. Theeffective panel image formed in the image formation area IF isrepresented as effective panel image PI. The heavy lines in FIG. 4( a)are shown for convenience to represent the boundaries (perimeter) of theentirely white pattern image, and are not part of the actual effectivepanel image PI.

The condition of the screen 200 is shown in FIG. 4( b). In the exampleof FIG. 4( b), the entirely white pattern is projected onto an area onthe screen 200 bounded by the heavy lines. Since this area is an area onthe screen 200 onto which is projected image light corresponding to allareas in the image formation area IF of the liquid crystal panel 130,this area constitutes the total projection area (hereinafter “totalprojection area PA”). On the screen 200, an entirely white image isdisplayed within the total projection area PA, with no image light beingprojected in areas except for the total projection area PA. The heavylines in FIG. 4( b) are not actually present in the projected image, butare shown for convenience to represent the perimeter of the totalprojection area PA; this perimeter is termed the “total projection areaframe PF.” In this embodiment, the screen 200 has a black screen frame202 along its perimeter. In order to easily distinguish between thescreen frame 202 and the total projection area frame PF, in FIGS. 4( a)to 7(e), the screen frame 202 (and screen frame 202 i described later)are represented by broken lines.

In the example of FIG. 4( b), the zoom level is such that the totalprojection area PA is too small relative to the size of the screen 200.As will be apparent from trapezoidal distortion of the total projectionarea frame PF, trapezoidal distortion has occurred.

The image signal of the total projection area detection pattern isstored in a predetermined area of the internal memory 120. The totalprojection area detection pattern may be any pattern that enablesdetection of the total projection area PA.

In Step S404 (FIG. 3), the capture module 180 (FIG. 1) captures thetotal projection area PA and the screen 200, and creates a shootingimage SI taken of the total projection area PA and the screen 200. Thecapture module 180 has a CCD camera for creating the shooting image SI.The shooting image SI created by the capture module 180 is placed in theinternal memory 120 (FIG. 1) from which it is stored in a shooting imagememory 182 (FIG. 1). Of course, some other capture device could be usedinstead of a CCD camera.

The condition of the shooting image SI is shown in FIG. 4( c). The totalprojection area frame PF (which represents the perimeter of totalprojection area PA) and the screen frame 202 of the screen 200 arecaptured in the shooting image SI. In the following description, thetotal projection area frame on the image is denoted as PFi, and thescreen frame on the image as 202 i. The total projection area frame PFion the shooting image SI is substantially rectangular. The screen frame202 i, on the other hand, has trapezoidal distortion. This is becausethe optical axis of the lens of the CCD camera of the capture module 180is set substantially parallel to the optical axis of the projectionoptical system 150. In the example of FIG. 4( c), the optical axis ofthe CCD camera lens and the optical axis of the projection opticalsystem 150 are not set strictly parallel, and the total projection areaframe PFi has slight trapezoidal distortion.

In FIGS. 4( a) to 4(c), there are shown coordinate systems establishedfor the liquid crystal panel 130, the screen 200, and the capture module180, respectively; these are denoted respectively as the liquid crystalpanel coordinate system Cp, the screen coordinate system Cs, and thecapture module coordinate system Cc. The liquid crystal panel coordinatesystem Cp is a coordinate system on a plane parallel to the panelsurface of the liquid crystal panel 130 having the image formation areaIF. The screen coordinate system Cs is a coordinate system on a planeparallel to the screen 200. The capture module coordinate system Cc is acoordinate system on a plane perpendicular to the optical axis of theCCD camera lens of the capture module 180.

In Step S406 (FIG. 3), the image region detector 123 (FIG. 1) analyzesthe image data of the shooting image SI stored in the shooting imagememory 182 and detects the total projection area frame PFi and screenframe 202 i. Detection of the total projection area frame PFi and screenframe 202 i is carried out by means of measuring the contrast ratio ofthe shooting image SI and extracting pixels with large contrast ratio.

Specifically, the total projection area frame PFi and screen frame 202 iare detected in the pixels making up the shooting image SI as locations(coordinates) of pixels in the capture module coordinate system Cc. Inthis embodiment, the coordinates of the four vertices of the totalprojection area frame PFi and the screen frame 202 i respectively aredetermined. That is, the coordinates of vertices a1-a4 and verticesb1-b4 shown in FIG. 4( c) are determined.

In Step S408 (FIG. 3), the standard transformation module 127 performsprojective transformation of the total projection area frame PFi and thescreen frame 202 i. FIGS. 5( a) and 5(b) are diagrams showing conceptionof projective transformation of the total projection area frame PFi andthe screen frame 202 i. The shooting image SI is shown in FIG. 5( a),while the image after projective transformation (transformed image SIt)is shown in FIG. 5( b). Here, projective transformation refers totransformation of coordinates representing the total projection areaframe PFi and the screen frame 202 i in the capture module coordinatesystem Cc into coordinates on a standard coordinate system. Thisprojective transformation is done in order to compensate formisalignment of the optical axis of the capture module 180 CCD cameralens and the optical axis of the projection optical system 150. In thisembodiment, the liquid crystal panel coordinate system Cp is used as thestandard coordinate system.

Where the projective transformation is designated as φ, when coordinates(x, y) are transformed in coordinates (u, v) by means of projectivetransformation φ, the coordinates (u, v) derived by projectivetransformation are represented by the following equations.u=(ax+by+c)/(gx+hy+1)v=(dx+ey+f)/(gx+hy+1)where a, b, c, d, e, f, g, and h are constants.

First, a projective transformation φ that transforms the coordinates ofthe four vertices a1-a4 of the total projection area frame PFi in thecapture module coordinate system Cc to coordinates in the liquid crystalpanel coordinate system Cp is calculated. This projective transformationis specified uniquely. Here, in this embodiment, as shown in FIG. 5( b),coordinates of the four vertices at1-at4 of the total projection areaframe PFiT after the projective transformation in the liquid crystalpanel coordinate system Cp are established respectively at at1 (0, 0),at2 (1023, 0), at3 (0, 767), and at4 (1023, 767). The coordinates areestablished as above for the purpose of convenience in calculation, byproviding correspondence with the resolution of the liquid crystal panel130 used in this embodiment. The coordinates of the four vertices of thetotal projection area frame PFiT after projective transformation neednot necessarily correspond to liquid crystal panel 130 resolution.

Next, using the derived projective transformation φ, the coordinates ofthe four vertices b1-b4 of the screen frame 202 i in the capture modulecoordinate system Cc are transformed into coordinates in the liquidcrystal panel coordinate system Cp, to derive a projective-transformedscreen frame 202 iT. The four vertices of the projective-transformedscreen frame 202 iT are represented by bt1-bt4 as shown in FIG. 5( b).In this way, the relative relationship of the total projection areaframe PFiT and screen frame 202 iT in the liquid crystal panelcoordinate system Cp are calculated.

In the following description, the projective-transformed totalprojection area frame PFiT is simply termed total projection area framePFiT, and the projective-transformed screen frame 202 iT is simplytermed screen frame 202 iT. The process starting with Step S408 ismerely one of calculation using coordinates; there is no need to createan image after transformation. Thus, in FIG. 5( b) and followingdrawings, lines showing actual image borders are not represented.

In Step S410 (FIG. 3), the best zoom level calculator 124 (FIG. 1)calculates a best zoom level. Here, best zoom level refers to the zoomlevel at which, when carrying out keystone correction while avoiding adrop in resolution of the effective panel image PI formed on the panelsurface of the liquid crystal panel 130, the image on the screen 200 canbe displayed as large as possible. Best zoom level is discussed furtherbelow.

FIGS. 6( a) to 6(c) are diagrams showing an example of projectionconditions after the zoom adjustment/keystone correction process. Thatis, the zoom adjustment/keystone correction process is executed so as toproduce the condition shown in FIGS. 6( a) to 6(c). FIGS. 6( a) to 6(c)correspond to FIGS. 4( a) to 4(c). Specifically, FIG. 6( a) representsthe condition of the liquid crystal panel 130, and FIG. 6( b) thecondition of the screen 200. For reference, FIG. 6( c) represents theshooting image SI where the projection condition after the zoomadjustment/keystone correction process has been captured by the capturemodule 180.

As shown in FIG. 6( b), the best zoom level is the zoom level at whichthe total projection area PA encompasses the screen 200, and theperimeter of the total projection area PA contacts the perimeter of thescreen 200 (the screen frame 202). The reason for this is as follows.

As shown in FIG. 6( b), keystone correction in this embodiment isintended to perform correction of an image so that the image isprojected exclusively onto a revised projection area RA that is a partarea of the total projection area PA falling within on the screen 200.Thus, as shown in FIG. 6( a), the effective panel image PI is formedexclusively within an area (represented as the revised image formationarea RIF) inside the image formation area IF on the panel surface of theliquid crystal panel 130, which area corresponds to the revisedprojection area RA. In areas excluding the revised image formation areaRIF in the image formation area IF, a wholly black image is formed sothat illuminating light emitted by the illumination optical system 140is not transmitted.

Since the revised projection area RA is an area that is part of thetotal projection area PA, if the total projection area PA does notencompass the screen 200, i.e. if zoom level is lower than the levelshown in FIG. 6( b), there will be an area of non-projection of imagelight on the screen 200. Thus, the image on the screen will be smaller.Accordingly, if the total projection area PA does not encompass thescreen 200, zoom level is not at the best level.

In order to avoid lower resolution of the effective panel image PI, itis preferable to make the revised image formation area RIF as large aspossible. The proportion of the total projection area PA occupied by therevised projection area RA is at its greatest when, with the totalprojection area PA encompassing the screen 200, the perimeter of thetotal projection area PA is in contact with the screen frame 202.Accordingly, at this time the revised image formation area RIF will beat its largest, and the zoom level at this time will the best zoomlevel.

FIGS. 7( a) to 7(e) are diagrams showing conception of calculation ofbest zoom level. Based on the concept outlined above, calculation ofbest zoom level is carried out using the total projection area framePFiT and screen frame 202 iT in the liquid crystal panel coordinatesystem Cp calculated in Step S408 (FIG. 3). Specifically, it is carriedout by enlarging or reducing the total projection area frame PFiTcentered on a predetermined zoom center ZC, deriving a bestzoom-adjusted total projection area frame PFiZb; and calculating thefactor of the enlargement or reduction (hereinafter best factor Mb).Here, the best zoom-adjusted total projection area frame PFiZb refers toa zoom-adjusted total projection area frame PFiZ derived by enlargementor reduction of the total projection area frame PFiT centered on thezoom center ZC, which frame encompasses the screen frame 202 iT andcontacts the screen frame 202 iT. The best zoom-adjusted totalprojection area frame PFiZb can be derived by deriving fourzoom-adjusted total projection area frames PFiZ respectively contactingthe four vertices of the screen frame 202 iT, and selecting the best oneof the four that has the zoom level furthest towards the wide end.

In FIG. 7( a) are shown the total projection area frame PFiT, the screenframe 202 iT, and the zoom center ZC in the liquid crystal panelcoordinate system Cp. The zoom center ZC is determined based on therelationship of the liquid crystal panel 130 and the zoom lens 152 ofthe projection optical system 150, and is not necessarily coincide withthe center of the image formation area IF of the liquid crystal panel130. The location of the zoom center ZC is stored in advance in apredetermined area of the internal memory 120, in the form ofcoordinates in the liquid crystal panel coordinate system Cp. The bestzoom level calculator 124 reads out the coordinates for the zoom centerZC that have been stored in the internal memory 120. Coordinates for thezoom center ZC in the liquid crystal panel coordinate system Cp may beestablished by making measurements on a per-product basis. By so doing,individual differences among products can be corrected, and processingcan be carried out accurately.

FIGS. 7( b) to 7(e) show enlargement of the total projection area framePFiT, centered on the zoom center ZC. In FIGS. 7( b) to 7(e), fourzoom-adjusted total projection area frames PFiZ that contactrespectively the four vertices bt1-bt4 of the screen frame 202 iT areindicated by dashed lines. Of these four zoom-adjusted total projectionarea frames PFiZ, the zoom-adjusted total projection area frame PFiZthat contacts vertex bt3 shown in FIG. 7( e) is that having the zoomlevel furthest towards the wide-angle end. Accordingly, this is the bestzoom-adjusted total projection area frame PFiZb. The other zoom-adjustedtotal projection area frames PFiZ shown in FIGS. 7( b) to 7(d) do notencompass the screen frame 202 iT. At these three zoom levels, there areareas on the screen 200 onto which image light is not projected (areascorresponding to the hatched areas in the drawing), so these do notrepresent the best zoom level.

If the zoom level were pushed further to the wide-angle end beyond thebest zoom-adjusted total projection area frame PFiZb shown in FIG. 7(e), the zoom-adjusted total projection area frame PFiZ and the screenframe 202 iT would no longer be in contact, and as such would notrepresent the best zoom level.

Once the best zoom-adjusted total projection area frame PFiZb has beenderived, the enlargement factor to the total projection area frame PFiT(best factor Mb) is calculated.

In Step S412 (FIG. 3), the zoom level detector 156 (FIG. 1) detects thecurrent zoom level. Detection of zoom level is carried out by detectingthe zoom encoder value described previously, and calculating a zoomlevel value based on the zoom encoder value. The current zoom levelvalue so calculated is designated as Zp.

In Step S414 (FIG. 3), the zoom adjustment module 125 (FIG. 1) executeszoom adjustment. Zoom adjustment is carried out by making the zoom levelvalue the value corresponding to the best zoom level (hereinafter termed“best zoom level value”). The best zoom level value is calculated bymultiplying the best factor Mb calculated in Step S410 by the currentzoom level value Zp calculated in Step S412. That is, the best zoomlevel value is calculated with the following equation.Best zoom level value=(Current zoom level value Zp)×(Best factor Mb)

The zoom adjustment module 125 controls the zoom lens driver 154 toperform zoom adjustment so that the zoom level value equals the bestzoom level value. This can be carried out through location monitoring bymeans of polling using the zoom encoder value described previously.

In Step S416 (FIG. 3), the keystone correction module 126 (FIG. 1)executes keystone correction. As described previously with reference toFIG. 6( a), keystone correction in this embodiment is carried out byforming the effective panel image PI exclusively in the revised imageformation area RIF in the image formation area IF of the liquid crystalpanel 130 corresponding to the revised projection area RA on the screen,in order for the image to be projected exclusively into the revisedprojection area RA that is a part area of the total projection area PAfalling within the screen 200.

The following description with regard to this point makes reference toFIG. 7( e) and FIG. 6( b). The area bounded by the best zoom-adjustedtotal projection area frame PFiZb shown in FIG. 7( e) corresponds to thetotal projection area PA at the best zoom level shown in FIG. 6( b). Thearea bounded by the screen frame 202 iT in FIG. 7( e) corresponds to therevised projection area RA of FIG. 6( b). Accordingly, where the shapeof the image in the area bounded by the best zoom-adjusted totalprojection area frame PFiZb is corrected to the shape of the areabounded by the screen frame 202 iT, the image will be displayed fittingwithin the screen frame 202 of the screen 200.

Since FIG. 7( e) represents the condition in the liquid crystal panelcoordinate system Cp, if the area bounded by the best zoom-adjustedtotal projection area frame PFiZb is realized on the liquid crystalpanel 130, the area bounded by the screen frame 202 iT will correspondto the revised image formation area RIF (FIG. 6( a)). Accordingly,keystone correction can be carried out by deriving a transformation thatmakes the best zoom-adjusted total projection area frame PFiZb conformto the screen frame 202 iT, and using the transformation to transformthe input signal.

As shown in FIG. 6( a), the revised image formation area RIF in theimage formation area IF of the liquid crystal panel 130 (area shown byhatching) corresponds to the area bounded by the screen frame 202 iTshown in FIG. 7( e). The perimeter of the revised image formation areaRIF contacts the perimeter of the image formation area IF, at a pointcorresponding to the contact point of the best zoom-adjusted totalprojection area frame PFiZb with the screen frame 202 iT.

After the zoom adjustment/keystone correction process, the revisedprojection area RA fits perfectly within the screen frame 202 of thescreen 200, as shown in FIG. 6( b). Accordingly, it will be understoodthat the zoom level is at the best zoom level, and that keystonecorrection has been carried out. Image light is not projected onto areasother than the revised projection area RA within the total projectionarea PA. Naturally, as shown in FIG. 6( c), the shooting image SI fitswithin the screen frame 202 of the screen 200.

As described hereinabove, the projector 100 of this embodiment can carryout a zoom adjustment/keystone correction process. Since the revisedimage formation area RIF in the image formation area IF on the liquidcrystal panel 130 has been established so as to be as large as possible,a drop in resolution of the effective panel image PI can be avoided.Also, since the process of test pattern projection, image capture,determination and zoom adjustment is not executed repeatedly, zoomadjustment and keystone correction can be carried out quickly andautomatically. Accordingly, the projector 100 of this embodiment cancarry out zoom adjustment and keystone correction quickly andautomatically, while avoiding drop in resolution.

B. Variations

The present invention is not limited to the embodiments and aspectsdescribed above. The present invention may be worked in various aspectswithin limits that involve no departure from the spirit of theinvention; for example, the following variations are possible.

B1. Variation 1

The projector 100 may additionally comprise a lens shifting module thatcan shift the zoom lens 152 in the direction perpendicular to theoptical axis of the projection optical system 150; and a center locationshifting module that shifts the zoom center ZC in accordance withshifting of the zoom lens 152 by the lens shifting module. By means ofthis arrangement, the projector 100, by means of shifting the zoom lens152, can shift the total projection area PA in the directionperpendicular to the optical axis of the projection optical system 150.Accordingly, the procedure for positioning the projector 100 can be madeeasier. Even if the zoom lens 152 has shifted, the zoom center ZC can beshifted in accordance with the shift of the zoom lens 152, whereby anaccurate zoom adjustment/keystone correction process is possible. Therelationship between shift of the zoom lens 152 and shift of the zoomcenter ZC can be measured in advance, and stored in a predetermined areaof the internal memory 120.

B2. Variation 2

The projector 100 may be constituted so as to calculate the revisedimage formation area RIF while the zoom adjustment module 125 iscontrolling the zoom lens driver 154 in order to adjust the zoom lens152 in the zoom adjustment/keystone correction process. With thisarrangement, keystone correction is carried out in parallel with zoomlens 152 adjustment, which is a mechanical operation, whereby theprocess can be made even faster.

B3. Variation 3

In the embodiment hereinabove, the best zoom level is designated as thezoom level at which the total projection area PA encompasses the screen200 and the perimeter of the total projection area PA contacts theperimeter of the screen frame 202; however, “contact” herein need not belimited to a state of exact contact, but may include a state ofsubstantial contact. That is, the best zoom-adjusted total projectionarea frame PFiZb shown in FIG. 7( e) need not be exactly contact withthe screen frame 202 iT, but may instead be separated from it by adistance of about three pixels in the liquid crystal panel 130.

B4. Variation 4

Whereas in the embodiment hereinabove the best zoom level is designatedas the zoom level at which the total projection area PA encompasses thescreen 200 and the perimeter of the total projection area PA contactsthe perimeter of the screen frame 202, such “contact” is not limited tocontact at single point, but can include cases of contact along one orseveral sides.

B5. Variation 5

Whereas in the embodiment hereinabove, projective transformation of thetotal projection area frame PFi and the screen frame 202 i is carriedout with the liquid crystal panel coordinate system Cp as the standardcoordinate system, projective transformation may instead be carried outwith some other coordinate system as the standard coordinate system.Also, it is not always necessary to carry out projective transformation;it is possible to dispense with the process.

B6. Variation 6

Whereas in the embodiment hereinabove, variable resistance is used todetect zoom level, but zoom level could instead be detected by someother method. For example, it would be possible to attach a rotaryencoder to the zoom lens 152, and to detect zoom level from the outputvalue of the rotary encoder. Alternatively, it would be possible to usea stepping motor as the zoom lens driver 154, and to detect zoom levelfrom the extent of drive thereof. It would also be possible to capturethe total projection area PA with the capture module 180, and detect thezoom level from the size of the total projection area PA in the shootingimage SI.

B7. Variation 7

Whereas in the embodiment hereinabove, during zoom adjustment,adjustment of the zoom lens 152 in order to make the zoom level valueequal to the best zoom level value is carried out through locationmonitoring by means of polling using zoom encoder values, it may insteadbe carried out by some other method. For example, it would be possibleto attach a rotary encoder to the zoom lens 152, and to perform zoomadjustment through location monitoring by means of polling using therotary encoder. Alternatively, it would be possible to use a steppingmotor as the zoom lens driver 154, and to carry out zoom adjustmentbased on the extent of drive thereof. Also, a motor drive time intervalmay be calculated from drive speed of the zoom lens 152 measured inadvance, and zoom adjustment carried out by driving the motor for thespecified time interval.

B8. Variation 8

Whereas in the embodiment hereinabove, keystone correction is carriedout by means of transformation so as to align the best zoom-adjustedtotal projection area frame PFiZb with the screen frame 202 iT, keystonecorrection may be carried out by some other method instead. For example,it may be carried out using a distance sensor or angle sensor.

B9. Variation 9

Whereas in the embodiment hereinabove, best zoom level is calculated bymeans of calculations using the screen frame 202 iT and the totalprojection area frame PFiT, it would instead be possible to derive bestzoom level by actually driving the zoom lens 152 to vary the zoom level,and analyzing the shooting image SI taken by the capture module 180.

B10. Variation 10

Whereas in the embodiment hereinabove, the zoom level value of thebaseline zoom level is assigned a baseline value of 1, with the zoomlevel value of any zoom level being represented in terms of theenlargement factor ratio thereof to the baseline zoom level, zoom levelvalue may be represented by some other method instead. For example, itwould be possible to represent zoom level assigning a zoom level valueof 0 to the zoom level furthest to the telephoto end and a zoom levelvalue of 255 to the zoom level furthest to the wide angle end.

B11. Variation 11

Whereas in the embodiment hereinabove, only a single liquid crystalpanel 130 is shown, it would be possible to provide a plurality ofliquid crystal panels 130 for a plurality of color components. Anelectro-optical device other than a liquid crystal panel (e.g. a DMD)may also be used.

B12. Variation 12

Whereas in the embodiment hereinabove, a screen 200 is used as theprojection surface, but it would be possible to use some other surfaceas the projection surface. For example, where the walls of the room arewhite, the wall may be used as the projection surface, by drawing arectangular frame on the wall with black lines created with tape orpaint. Alternatively, a rectangular frame may be drawn with black lineson a white board, and the white board used as the projection surface.

The color of the projection surface is not limited to one in which theframe is black and the areas to the inside and outside of the frame arewhite; a white frame with black areas to the inside and outside of theframe would be possible as well. For example, a rectangular frame may bedrawn with chalk on a blackboard, and the blackboard used as theprojection surface.

In the present invention, projection surface colors are not limited towhite and black, but may consist of any color combination whose colorshave a predetermined contrast ratio between the color of the frame thecolor of the areas to the inside and outside of the frame.

1. A projector for displaying an image on a projection surfacecomprising: a light source configured to emit light; an image formationpanel configured to form an effective panel image for modulating lightemitted by the light source into effective image light representing animage, the image formation panel being formed in an image formation areaof a panel surface; and an image processor including a zoom adjustingmodule and a keystone correcting module, the image processor configuredto correct for trapezoidal distortion on the projection surface by (1)adjusting the zoom level of a zoom lens to a target zoom level, and (2)performing a keystone correction; the image processor correcting fortrapezoidal distortion of the image displayed on the projection surfaceby means of forming the effective panel image in a revised imageformation area, the revised image formation area being part of the imageformation area of the panel surface; the zoom adjusting module adjustingthe zoom level to the target zoom level; the target zoom level being azoom level in which a total projection area encompasses the projectionsurface, and in which a perimeter of the total projection area contactsthe perimeter of the projection surface at one or more contact points,the total projection area being an area onto which is projected imagelight corresponding to all areas of the image formation area of thepanel surface; and the keystone correcting module performing a keystonecorrection such that the perimeter of the revised image formation areacontacts the perimeter of the image formation area of the panel surface,the contact between the revised image formation area and the perimeterof the image formation area of the panel surface being at a point on theperimeter of the image formation area of the panel surface correspondingto the contact point of the perimeter of the total projection area withthe perimeter of the projection surface.
 2. A projector according toclaim 1, further comprising: a zoom level detecting module configured todetect zoom level; an image capture module configured to capture aprojection status image including an image of the projection surface andan image of the total projection area; an image region detecting moduleconfigured to detect within the projection status image a projectionsurface image region representing the projection surface and an totalprojection area image region representing the total projection area; anda target image region calculating module configured to calculate atarget total projection area image region, the target total projectionarea image region representing the total projection area image regionmagnified or reduced centered on a predetermined zoom center locationsuch that the target total projection area image region encompasses theprojection surface image region, and that a perimeter of the targettotal projection area image region contacts a perimeter of theprojection surface image region, wherein the zoom adjusting modulemultiplies zoom level detected by the zoom level detecting module, by amagnification ratio or reduction ratio of the target total projectionarea image region with respect to the total projection area imageregion, to calculate the target zoom level, and the keystone correctingmodule calculates the revised image formation area by means oftransformation of a perimeter of the image formation area of the panelsurface such that the perimeter of the target total projection areaimage region conforms to the perimeter of the projection surface imageregion.
 3. A projector according to claim 2, further comprising: astandard transformation module configured to transform the projectionsurface image region and the total projection area image region detectedby the image region detecting module to a predetermined standardcoordinate system, wherein the target image region calculating modulecalculates the target projection area image region by use of theprojection surface image region and the total projection area imageregion transformed by the standard transformation module.
 4. A projectoraccording to claim 3, wherein the standard coordinate system is acoordinate system in a plane parallel to the panel surface having theimage formation area.
 5. A projector according to claim 2, wherein thezoom center location is a predetermined location other than the centerof the image formation area of the panel surface.
 6. A projectoraccording to claim 2, further comprising: a lens shifting moduleconfigured to shift the zoom lens in a direction perpendicular to theoptical axis of the zoom lens; and a center location shifting moduleconfigured to shift the zoom center location depending on shift of thezoom lens by the lens shifting module.
 7. A projector according to claim2, wherein the keystone correcting module performs calculation of therevised image formation area while the zoom adjusting module isadjusting the zoom lens.
 8. An image correction method for correcting animage in a projector for displaying an image on a projection surface,the method comprising the steps of (a) forming an effective panel imagein an image formation area of a panel surface, the effective panel imagebeing an image for modulating light emitted by a light source intoeffective image light representing an image; (b) adjusting zoom level ofa zoom lens for enlarged projection of image light; and (c) correctingtrapezoidal distortion of the image displayed on the projection surfaceby means of forming the effective panel image in a revised imageformation area, the revised image formation area being part of the imageformation area of the panel surface, wherein the step (b) includes thestep of adjusting the zoom level to a target zoom level in which a totalprojection area encompasses the projection surface and in which aperimeter of the total projection area contacts the perimeter of theprojection surface at one or more contact points, the total projectionarea being an area onto which is projected image light corresponding toall areas of the image formation area of the panel surface, and the step(c) includes the step of performing correction such that the perimeterof the revised image formation area contacts the perimeter of the imageformation area of the panel surface at a point on the perimeter of theimage formation area of the panel surface corresponding to the contactpoint of the perimeter of the total projection area with the perimeterof the projection surface.
 9. A computer program product for correctingan image in a projector for displaying an image on a projection surface,the projector comprising a light source configured to emit light, and animage formation panel configured to form in an image formation area of apanel surface an effective panel image for modulating light emitted bythe light source into effective image light representing an image, thecomputer program product comprising: a computer readable medium; and acomputer program stored on the computer readable medium, the computerprogram including: a first program for causing a computer in theprojector to adjust zoom level of a zoom lens for enlarged projection ofimage light; and a second program for causing the computer to correcttrapezoidal distortion of the image displayed on the projection surfaceby means of forming the effective panel image in a revised imageformation area, the revised image formation area being part of the imageformation area of the panel surface, wherein the first program includesa program for causing the computer to adjust the zoom level to a targetzoom level in which a total projection area encompasses the projectionsurface and in which a perimeter of the total projection area contactsthe perimeter of the projection surface at one or more contact points,the total projection area being an area onto which is projected imagelight corresponding to all areas of the image formation area of thepanel surface, and the second program includes a program for causing thecomputer to perform correction such that the perimeter of the revisedimage formation area contacts the perimeter of the image formation areaof the panel surface at a point on the perimeter of the image formationarea of the panel surface corresponding to the contact point of theperimeter of the total projection area with the perimeter of theprojection surface.